1. Field of the Invention
This invention relates to a resist composition predominantly comprising a novolak resin serving as both an alkali-soluble resin and a photosensitive agent, the composition being useful as a positive resist having many advantages of uniformity, sensitivity, resolution, heat resistance and film retentivity.
2. Prior Art
Prior art novolak system resist compositions use a novolak resin and a photosensitive agent as two main components. In order that resists have high resolution, heat resistance and film retentivity and match with the wavelength of a light source in various exposure equipment, a number of improvements have been made from both the sides of novolak resin and photosensitive agent. One approach from the novolak resin side was to reduce the average molecular weight of novolak resin on synthesis whereby the resulting resist was improved in resolution and in sensitivity at the sacrifice of heat resistance and film retentivity (see Japanese Patent Application Kokai No. 2-275955 or EP 0358871A2). Then an attempt was made to remove low molecular weight novolak components from the synthesized novolak resin by suitable means such as reprecipitation. One exemplary approach from the photosensitive agent side, which is based on the fact that resists containing conventionally used benzophenone photosensitive agents are less transmissive to light as the light source of an exposure equipment varies from g-rays to i-rays, was the use of non-benzophenone photosensitive agents having minimal absorption of i-rays (see Nikkei Micro-Device, April 1992, page 45).
While resists with higher resolution might be obtained by combining these approaches, a number of steps must be added to the resist manufacturing process, resulting in the disadvantage of increased cost.